Human papillomavirus (HPV) infection of the cervix initiates the development of cervical cancer. Vaccination has the potential to prevent cervical cancer by preventing primary HPV infection and by eliminating persistent lesions. The ideal vaccine would induce therapeutic as well as protective immunity. The best animal model for therapeutic vaccine development is the cottontail rabbit papillomavirus (CRPV)-rabbit model. Live recombinant vesicular stomatitis viruses (rVSV) expressing foreign viral proteins have successfully protected animals against challenges with several human viruses. We recently generated an rVSV vector expressing the CRPV E6 tumor antigen and used it to vaccinate rabbits with well-established tumors (papillomas) in a preliminary experiment. The treatment induced dramatic therapeutic outcomes including the complete and permanent regression of all disease in some rabbits with a total papilloma burden of 4 cm3, as compared to no regression in the controls. The hypothesis of this application is that the rVSV-E6 vaccine can be improved to induce more rapid and more universal regression. It is based on the observation that the original vaccine expressed a relatively low level of E6 protein and that revaccination with the same rVSV-E6 was probably not effective, due to VSV-specific neutralizing antibodies induced by primary vaccination. The efficacy of the rVSV-E6 could also be improved by modifying the E6 gene to encode a ubiquitin-E6 fusion protein (UbE6), based on our findings, using CRPV DNA vaccines, that a UbE6 fused gene was markedly more effective than the unfused E6 gene. The specific aims are to repeat the preliminary experiment with larger group size and all appropriate controls; to determine if more rapid and more universal tumor clearance can be obtained using VSV vectors giving higher-level expression of E6 or expressing UbE6, using an efficient VSV-E6 boosting vector with the VSV envelope gene from a heterologous serotype, or using a completely heterologous viral vector (adenovirus). We will determine if the most effective therapeutic vaccine also induces protective immunity. The data provided by this investigation are likely to aid in the development a highly effective HPV vaccine to protect women against cervical cancer.